I guess this question is raised from time to time – now I am asking ;)
As far as I understand, there is still no own LaTeX3 format because the
code just is not ready. But expl3 is more or less stable and some
important packages (e.g. fontspec) make heavy use of it causing many
people to load expl3 at the beginning of their document. As this is
somewhat time-consuming, Philipp Stephani suggested about a month ago on
the lualatex-dev list the introduction of a "LaTeX 2.2" format with
expl3 and xpackages (and fontspec) preloaded.
So what is the "official" meaning of the LaTeX3 team? Are there any
plans for a test format? Or is it not intended/possible/ ?
Such a format could be a very good test for stability and useability,
would show progress to the users and could be distributed via TLcontrib
so the normal user would not be confused by this, but the experienced
user could easily test and try LaTeX3.